1. Field of the Invention
The present invention relates to a circuit which determines whether or not the connection polarities of left and right loudspeakers connected to a stereo amplifier or the like coincide with those of the stereo amplifier, an audio circuit having such a determining function, and an audio circuit having a function of, when coincidence of the connection polarities fails to be attained, switching over the polarities.
The present application is based on Japanese Patent Application No. Hei. 10-286085, which is incorporated herein by reference.
2. Description of the Related Art
In a stereo reproduction system, the polarities of left and right loudspeakers must be coincident with those of speaker terminals of a stereo amplifier. The state of coincidence of the connection polarities of left and right loudspeakers means a state where all of plus and minus terminals of left and right loudspeakers are respectively connected to plus and minus speaker terminals of left and right channels of an amplifier or the like in a perfectly coincident manner, or in a completely reversed manner. The state of incoincidence of the connection polarities of left and right loudspeakers means a state where plus and minus terminals of one of left and right loudspeakers are respectively connected to plus and minus speaker terminals of the one of left and right channels of an amplifier or the like in a coincident manner and plus and minus terminals of the other one of the left and right loudspeakers are respectively connected to the plus and minus speaker terminals of the other one of left and right channels of the amplifier in a reversed manner.
As a method of determining whether or not coincidence of the connection polarities of left and right loudspeakers are attained, known is a method in which one test signal is reproduced from both the left and right loudspeakers. When the reproduced sound is localized at the midpoint between the left and right loudspeakers, the reproduced sounds of the left and right loudspeakers are positive-phase, and it is therefore determined that coincidence of the connection polarities of the loudspeakers is attained. The connections of the loudspeakers are not required to be changed. By contrast, when the reproduced sound is localized outside the left and right loudspeakers, the reproduced sounds of the left and right loudspeakers are negative-phase, and it is therefore determined that incoincidence of the connection polarities of the loudspeakers occurs. The connection polarity of the loudspeaker of one channel must be reversed.
In the above determining method, it is difficult to determine whether or not coincidence of the connection polarities of left and right loudspeakers is attained because of the following reasons.
(a) Problem due to absolute evaluation: Only one sound is used in determining whether the sound is positive-phase or negative-phase, and hence the determination is based on absolute evaluation. Since there is no reference for comparison, skills are required for the determination.
(b) Problem due to standing wave: In the case where a test signal having only one frequency component is used, when the frequency is close to that of the standing wave of the room, interference between the test signal and the standing wave causes polarities to be incorrectly determined.
(c) Problem due to arrangement of loudspeakers: When a test signal has a higher signal, the wavelength is shorter. In the case where the distances between the discriminator and left and right loudspeakers are different from each other, a difference of one half wavelength causes negative-phase, and a difference of one wavelength causes positive-phase. For example, a signal of 1 kHz has a wavelength of 1 msec. Since the velocity of sound is 340 m/sec, the wavelength corresponds to a distance of 34 cm. A difference of such a distance easily occurs depending on the placement of loudspeakers or the listening position. In the case of a karaoke apparatus, particularly, loudspeakers are often placed in a bilaterally asymmetrical manner, and hence this problem easily occurs.
In the related art, it is difficult to determine whether or not coincidence of the connection polarities of left and right loudspeakers is attained because of the above reasons. Only a skilled person can correctly conduct the determination.
It is an object of the present invention to provide a polarity determining circuit for loudspeakers, and an audio circuit having functions of determining polarities of loudspeakers and switching the polarities which can solve the problems of the related art and which can easily and correctly determine whether or not coincidence of the connection polarities of left and right loudspeakers is attained.
The polarity determining circuit for loudspeakers of the present invention comprises: a test signal generator which generates a test signal; a signal switching device which, based on a switching operation of a user, selectively outputs either one of a positive-phase signal of the test signal and a negative-phase signal of the test signal; and left and right speaker terminals; wherein an output signal of the signal switching device is output from one of the left and right speaker terminals, and one of the positive-phase and negative-phase signals of the test signal is constantly output from the other of the left and right speaker terminals.
According to the polarity determining circuit, based on a switching operation of the user, the test signal can be reproduced while being switched to positive-phase or negative-phase for one of the left and right channels. Therefore, relative evaluation can be conducted by comparing the test signals of positive-phase and negative-phase with each other. Consequently, it is possible to easily determine whether the reproduced sound is localized between left and right loudspeakers (i.e., coincidence of the connection polarities of the left and right loudspeakers is attained) or outside the loudspeakers (i.e., coincidence is not attained).
An audio circuit having a function of determining polarities of loudspeakers of the present invention comprises: a test signal generator which generates a test signal; a signal switching device which, based on a switching operation of a user, selectively outputs either one of a positive-phase signal of the test signal and a negative-phase signal of the test signal; a selector which, based on a selecting operation of the user, selectively outputs either one of an output test signal of the signal switching device and a musical sound signal of one of left and right channels, as a signal of the one of the left and right channels, and which, interlocked with the output, selectively outputs either one of a constant output which is one of the positive-phase and negative-phase signals of the test signal, and a musical sound signal of another one of the left and right channels, as a signal of the other one of the left and right channels; and left and right speaker terminals from which the output signals of the left and right channels of the selector are respectively output.
According to the audio circuit, the test signal and the musical sound signal can be selectively output from the selector. In polarity determination using the test signal, when it is determined that coincidence of the connection polarities of the left and right loudspeakers is not attained, the connection between the speaker terminals of one of the left and right channels and the loudspeaker of the one of the left and right channels is changed (namely, the connection polarity is reversed), whereby coincidence of the connection polarities of the left and right loudspeakers can be attained.
The audio circuit having functions of determining polarities of loudspeakers and switching the polarities of the present invention comprises: a test signal generator which generates a test signal; a first signal switching device which, based on a switching operation of a user, selectively outputs either one of a positive-phase signal of the test signal and a negative-phase signal of the test signal; a selector which, based on a selecting operation of the user, selectively outputs either one of an output test signal of the first signal switching device and a musical sound signal of one of left and right channels, as a signal of the one of the left and right channels, and which, interlocked with the output, selectively outputs either one of a constant output which is one of the positive-phase and negative-phase signals of the test signal, and a musical sound signal of another one of the left and right channels, as a signal of the other one of the left and right channels; a second signal switching device which, based on the switching operation of the user, selectively outputs either one of a positive-phase signal of the output signal of the one of the left and right channels of the selector, and a negative-phase signal of the output signal; and left and right speaker terminals from which the output signal of the second signal switching device and the output signal of the other one of the left and right channels of the selector are respectively output.
According to the audio circuit, the test signal and the musical sound signal can be selectively output from the selector. In polarity determination using the test signal, when it is determined that coincidence of the connection polarities of the left and right loudspeakers is not attained, switchover of positive-phase/negative-phase is conducted by the second signal switching device on the side of the output of the selector, thereby enabling coincidence of the connection polarities of the left and right loudspeakers to be attained without changing connections between the speaker terminals and the loudspeakers.
The other audio circuit having functions of determining polarities of loudspeakers and switching the polarity of the present invention comprises: a test signal generator which generates a test signal; a first signal switching device which, based on a switching operation of a user, selectively outputs either one of a positive-phase signal of the test signal and a negative-phase signal of the test signal; a second signal switching device which, based on a selecting operation of the user, selectively outputs either one of a positive-phase signal of a musical sound signal of one of left and right channels and a negative-phase signal of the musical sound signal; a selector which, based on the selecting operation of the user, selectively outputs either one of an output signal of the second signal switching device, and the output test signal of the first signal switching device, that is, a constant output which is one of positive-phase and negative-phase signals of the test signal, as a signal of the one of the left and right channels, and which, interlocked with the output, selectively outputs either one of a musical sound signal of another one of the left and right channels, and a constant output which is one of the positive-phase and negative-phase signals of the test signal, that is, the output test signal of the first signal switching device, as a signal of the other one of the left and right channels; and left and right speaker terminals from which the output signals of the left and right channels of the selector are respectively output.
According to the audio circuit, the test signal and the musical sound signal can be selectively output from the selector. In polarity determination using the test signal, when it is determined that coincidence of the connection polarities of the left and right loudspeakers is not attained, switchover of positive-phase/negative-phase is conducted by the second signal switching device on the side of the input of the selector, thereby enabling coincidence of the connection polarities of the left and right loudspeakers to be attained without changing connections between the speaker terminals and the loudspeakers. In this case, the operation of the second signal switching device for switching over positive-phase/negative-phase of the musical sound signal can be interlocked with that of the first signal switching device for switching over positive-phase/negative-phase of the test signal (an interlocked operation is conducted so that, when the first signal switching device is positive-phase, the second signal switching device is also positive-phase, and, when the first signal switching device is negative-phase, the second signal switching device is also negative-phase). According to this configuration, when coincidence of the connection polarities of the left and right loudspeakers is attained by means of the first signal switching device using the test signal, the signals of the left and right channels are then switched to the musical sound signals so that the loudspeakers are used as they are.
The further audio circuit having functions of determining polarities of loudspeakers and switching the polarity of the present invention comprises: a test signal generator which generates a test signal; a selector which, based on a selecting operation of a user, selectively outputs either one of the test signal and a musical sound signal of one of left and right channels, as a signal of the one of the left and right channels, and which, interlocked with the output, selectively outputs either one of the test signal and a musical sound signal of another one of the left and right channels, as a signal of the other one of the left and right channels; a signal switching device which, based on a switching operation of the user, selectively outputs either one of a positive-phase signal of the output signal of the one of the left and right channels of said selector, and a negative-phase signal of the output signal; and left and right speaker terminals from which the output signal of said signal switching device and the output signal of the other one of the left and right channels of said selector are respectively output.
According to the audio circuit, polarity determination and polarity switching can be simultaneously conducted by the single signal switching device on the side of the output of the selector.
The test signal generator used in the present invention may comprise, for example, a white noise generator which generates a white noise signal, and a low-pass filter which receives the white noise signal, and which extracts a low-frequency component and outputs the low-frequency component as the test signal. According to this configuration, since the test signal having plural frequency components is used, determination is hardly affected by the standing wave of the room. Furthermore, since the test signal from which higher frequency components are cut away is used, determination is hardly affected by the manner of placement of loudspeakers, so that, in polarity determination, it is possible to easily determine whether the test sound is localized between the left and right loudspeakers or outside the loudspeakers. In order to enable determination to be further hardly affected by the manner of placement of loudspeakers or the listening position, preferably, the cut-off frequency of the low-pass filter is set to be, for example, about 300 Hz or lower. Since a human being can hardly sense a frequency of several tens hertz or lower, the test signal may be restricted to a signal of several tens hertz or higher.